MRI is a diagnostic modality that requires exposing patients to static, gradient, and radiofrequency (RF) electromagnetic fields. The U.S. FDA has issued guidelines for the safe application of the RF radiation used for MRI. We hypothesize that these guidelines may be unnecessarily restrictive resulting in prolonged imaging times and, therefore, inhibit the cost-effective utilization of MRI. Since the primary bioeffects of MRI are related to the thermogenic qualities of RF energy, the focus of this investigation is to examine the changes in temperature and physiologic responses produced by operating a 1.5 T MR scanner above recommended FDA guidelines for RF energy. Of further note is that "fast spin echo" pulse sequences have been recently designed that frequently have associated RF power requirements that easily exceed SARs of 4 to 8 W/kg (i.e., 10 to 20 times higher than the current SAR of 0.4 W/kg recommended by the FDA). These "fast spin echo" pulse sequences must be thoroughly studied before wide-spread clinical use. The specific aims of this project are: to determine temperature and physiologic responses produced by MRI of normal subjects, patients with normal thermoregulation, and patients with conditions associated with heat intolerance; to determine the temperature changes of thermal sensitive tissues (i.e., the testis and eye) produced by MRI; to determine the possible presence of surface thermal "hot spots" produced by MRI; and to determine the subjective perceptions of temperature and comfort related to the temperature changes caused by MRI. The methods include: measurement of "core" (sublingual pocket and urine), skin, superficial fat, muscle, scrotal, and corneal temperatures using the appropriate state-of-the-art techniques; measurement. of heart rate (fiber-optic pulse oximeter), blood pressure (oscillometric technique), respiratory rate (end-tidal carbon dioxide method), and skin blood flow (laser-Doppler velocimetry); determination of surface heating patterns by thermography; and assessment of the patients' subjective perceptions of temperature and comfort by means of a standardized questionnaire. The resulting information will provide significant and important data to help establish safe levels of exposure to the RF electromagnetic fields used for MRI and differentiate between patients that may or may not require continuous physiologic monitoring during MRI.